<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="app">
    =={{msg}}===computed===={{arr}}=={{total}}
    <input type="text" v-model.number="val" @keyup.enter="handle">
    <hr />
  </div>
  <script src="https://cdn.bootcdn.net/ajax/libs/vue/2.7.14/vue.min.js"></script>
  <script>
    var vm = new Vue({
      el: "#app",
      data: {
        msg: 'hello  vue',
        arr: [1, 2, 3, 4, 5],
        val: ''
      },
      methods: {
        handle () {
          this.arr.push(this.val)
        }
      },
      computed: {
        /* 计算属性 */
        /* 函数 并且函数有返回值====函数中的数据是【当前来说】基于data中的数据 */
        total () {
          /* 只要数据变化就会立即重新执行，初次进入也会立马执行 */
          return this.arr.reduce((sum, item) => sum + item, 0)
        }
      }
    })

    // console.log(vm, 2222);
  </script>
</body>

</html>